Field of the Invention
The present invention relates to a variable valve timing camshaft. More particularly, the present invention relates to a variable valve timing camshaft which is adapted to vary open/close timing of a valve.
Description of Related Art
Generally, an intake valve which is selectively opened or closed so as to supply fuel for combustion and an exhaust valve which is selectively opened or closed so as to exhaust exhaust gas formed by the combusted fuel are provided in a combustion chamber of an engine.
The determining of open/close timing of the valve (intake valve or exhaust valve) may depend on a shape of a cam, rotation speed of a camshaft, and so on.
In detail, the cam rotates together with the camshaft to drive the valve, and the camshaft rotates by receiving torque from an engine. In addition, the time from when opening of the valve is started to when closing of the valve is ended and the lift of the valve are determined according to the shape of the cam, and the time from when opening of the valve is started to when closing of the valve is ended and the repetition cycle of opening/closing the valve are determined according to the rotation speed of the camshaft.
The rotation speed of the camshaft is generally proportional to the rotation speed of the engine. In addition, the optimally required open/close timing of the valve is varied according to the rotation speed of the engine. Therefore, it is required that the open/close timing of the valve is suitably varied according to the rotation speed of engine. Particularly, output and fuel consumption of the engine can be improved and simultaneously exhaust gas can be decreased if the open/close timing of the intake valve is suitably varied according to driving conditions including the rotation speed of the engine.
Meanwhile, the open/close interval between valves which are respectively disposed at combustion chambers which are provided in the engine may be determined by a phase difference along a circumferential direction between cams which open/close each valve.
An apparatus for controlling the open/close timing of the valve is one such as a continuous variable valve timing (CVVT) apparatus. In addition, the CVVT apparatus is operated to control the rotation speed of the camshaft and vary a phase difference along a circumferential direction between the cams.
However, reactivity or durability may be deteriorated if a connection structure with or composition of the CVVT apparatus for controlling the open/close timing of the valve and the camshaft is complex. In addition, interference with surrounding devices may occur.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.